The invention relates to half bridge driver integrated circuits. More particularly, this invention relates to the preparation of a high voltage half bridge integrated circuit with level shifting input control where all complementary metal oxide semiconductor (CMOS) components have been replaced with N- and P-channel double diffused metal oxide semiconductor (DMOS) components.
A high voltage, half bridge integrated circuit (IC) with level shifting input control serves a very important function that is used ubiquitously in many areas of power and control electronics. Presently this function is integrated using full mask silicon on insulator (SOI) technology that requires numerous masking steps to implement.
A half bridge driver integrated circuit (IC), such as the one shown in FIG. 1 and identified by the numeral 1, typically comprises two, i.e., high and low, power metal oxide silicon (MOS) field effect transistor (FET) or insulated gate bipolar transistor (IGBT) switches 11, 12. The half bridge driver IC 1 further comprises a circuit 2 used for generating two square wave signals to control the timing of conduction time to power switches 11, 12. This circuit 2 is called a xe2x80x9cnon-overlapxe2x80x9d circuit since signals from circuit 2 conducted to power switches 11, 12 are controlled so that the switches 11, 12 do not xe2x80x9coverlap,xe2x80x9d that is they are not switching on at the same time. The dead time between the two signals avoids any cross conduction of the two power switches 11, 12 and prevents the simultaneous switching on of both these power switches 11, 12.
The half bridge driver IC 1 further comprises two high voltage level shifter MOSFET transistors 5a, 5b, each of these level shifter transistors being connected with a distinct current source 4a, 4b. Each of the distinct current sources receives separate Ion and Ioff voltage pulses from a circuit 3, called the pulse generator circuit, which is used to generate short voltage pulses. The pulse generator circuit 3 generates two short pulses to control the on time switch of the current sources 4a, 4b. Short pulses instead of long ones are used in order to reduce the level shifting power dissipation. Pulses from the pulse generator circuit 3 are sent to the two current sources 4a, 4b, which are switched on or off according to the input pulse.
Current passage is allowed from each current source 4a, 4b through respective transistors 5a, 5b, which may have ranges of up to a few hundred Volts and are used to communicate between the ground reference level and high voltage reference level, e.g., 500 Volt. These transistors 5a, 5b may sustain a high voltage across their drain and source. Other devices such as regular CMOS or DMOS are not able to handle such high voltage.
A pulse filter circuit 6 receives short current pulses initiated by the current sources and passed by the level shifter transistors. In its turn the pulse filter circuit 6 generates two voltage levels to activate a latch or flip flop 7 which, according to its received input signals, sends an on or off output signal to switch the high power switch 11 on and off even in the presence of a large common mode current arising from dv/dt coupling. A high side driver 8 is positioned between the latch 7 and the power switch 11 to drive the top power switch 11.
Moreover, a voltage step up circuit 13 is positioned to receive and to translate the square wave signal from the non-overlap circuit 2 to the low side driver circuit 9, which will drive the low power switch 12. The high side and low side drivers 8, 9 provide sufficient driving power capabilities for the half bridge power switches 11, 12, which may be integrated in the half bridge driver IC 1, to turn on or off the half bridge power switches 11, 12, which provide the high voltage square wave to its load as may be specified.
The half bridge driver IC 1 further comprises a bootstrap diode 16 that is connected on one side to a bootstrap capacitor 10, which in turn is connected to the pulse filter 6, the latch 7, the high driver 8, and in between the high transistor 11 and the low transistor 12. On the second side, the bootstrap diode 16 is connected to the low supply generator 14 for supplying voltage to the non-overlap circuit 2, the pulse generator circuit 3, and the step-up circuit 13.
It is important to note that in the present state of the art, low voltage circuits such as the non-overlap circuit 2, the pulse generator circuit 3, and the current sources 4 use a low threshold complementary MOS (CMOS) with a typical 1 Volt threshold. Other circuits and components, such as the pulse filter 6, the latch 7, the high side driver 8, and the low side driver 9 use a double diffused MOS (DMOS) rather than CMOS. DMOS components allow for higher supply of voltage, i.e., 12 Volt, to sufficiently drive the half bridge power switches 11, 12.
Different types of IC components, such as DMOS and CMOS, require more masking steps in the IC manufacturing process making the manufacturing of such a circuit much more expensive than the manufacture of a circuit having components of only one type since the manufacturer""s cost is somewhat proportional to the number of masking steps. Furthermore, the non-overlap circuit 2 and the pulse generator circuit 3 are implemented with the low supply generator 14 supplying voltage, e.g., 5 Volt, whereas circuits such as the pulse filter 6, the latch 7, the low side driver 9 and the high side driver 8 are implemented with higher supply voltages, e.g., 12 Volt. A supply generator 14 is required to provide low supply, i.e., 5 Volt, from a higher supply, e.g., 12 Volt. Furthermore, The voltage step up circuit 13 is required to translate signals from the non-overlap circuit 2 to the low side driver circuit 9. Those voltage supply differences make the design and the manufacture of such a circuit complicated, require larger area consumption by the IC, and make the circuit expensive to manufacture.
Finally, an additional problem exists in the pulse filter 6, which is shown in detail in FIG. 2. High threshold voltage P-channel DMOS transistors 20a, 20b are used in the manufacture of the pulse filter 6. Typically, the DM0S FET has a threshold voltage of 3.5 Volt for an N-channel and xe2x88x925 Volt for a P-channel. In order to turn one of the two P-channel DMOS transistors 20a, 20b on, at least the threshold voltage drop of the transistor 20 is required to be applied across one of the two resistors 21a, 21b connected to the gate of the DMOS transistor. When the voltage drop across resistors 21a, 21b is insufficient to turn on the DMOS transistor, the DMOS will not conduct. Therefore a voltage cannot be created across resistor 22 to turn on one of the inputs to the latch 7. Consequently the latch 7 will not provide the correct output and therefore will not work in the right state. Furthermore, low resistance is desired of both resistors 21a, 21b of the pulse filter 6 to maintain low voltage drop across them in the presence of a large common mode level shifting current arising from dv/dt coupling. On the other hand, high resistance is desired in order to utilize the low differential level shifting current to save power dissipation.
It would be advantageous to have a circuit having sufficient margin of output voltage swing and low differential current input. That circuit is less expensive to manufacture than those presently available and takes minimum footprint area.
The present invention introduces a low cost half bridge driver IC that overcomes the drawbacks of the prior art. In particular this invention introduces a half bridge driver IC, which is fabricated in the process technology with a minimum or reduced number of masking steps to implement all the blocks and without the use of the low threshold voltage CMOS. The inventive half bridge driver IC uses a universal 12 Volt supply for all the locks with reference to the ground or to the half bridge output. Furthermore, the low differential current from high voltage level shifter transistors of the inventive half bridge driver IC, can provide enough voltage swing to set or reset the latch when high threshold voltage DMOS are used in the pulse filter.